The invention relates to a charging device for electric vehicles comprising an external alternating voltage source and a motor vehicle with a high-voltage battery, wherein the motor vehicle has a low-voltage battery, a link circuit capacitor and a charging electronics unit with a charging voltage input and a supply voltage input.
Various demands, such as operating convenience, high user flexibility and high charging capacity, are placed on the charging device of an electric vehicle, which frequently lead to very complex and cost-intensive solutions. As a result, it is also more difficult to fulfill minimum requirements for longevity, robustness and customer availability. In this area of conflict are to be found circuits according to the prior art which are intended, for example, to limit the switch-on current, i.e. the inrush current, when a charging connection is made by plugging-in a charging cable and closing contactors. For example, the switch-on current can be limited by a resistor, which can be bypassed by switching a relay for example, after the switch-on current has occurred. On the one hand, limiting the switch-on current ensures the prescribed conformity, for example, with the CE label of safety and health-related products for guaranteeing the free movement of goods. On the other, additional losses, which mean a poorer charging efficiency when charging the electric vehicle, are associated with such a switch-on-current-limiting circuit.
An object of the invention is to provide an improved charging device for an electric vehicle.
This and other objects are achieved by a charging device comprising an external alternating current voltage source and a motor vehicle with a high-voltage battery, wherein the motor vehicle has a low-voltage battery, a link circuit capacitor and a charging electronics unit with a voltage input and a supply voltage input. The vehicle has a bidirectional auxiliary power supply with two interfaces. The first interface of the auxiliary power supply is connected in parallel with the link circuit capacitor and in parallel with the charging voltage input of the charging electronics unit. The second interface of the auxiliary power supple and the low-voltage battery are connected in parallel with the supply voltage input of the charging electronics unit.
According to the invention, the motor vehicle has a bidirectional auxiliary power supply with two interfaces. The first interface of the auxiliary power supply is connected in parallel with the link circuit capacitor and in parallel with the charging voltage input of the charging electronics unit. The second interface of the auxiliary power supply and the low-voltage battery are connected in parallel with the supply voltage input of the charging electronics unit.
The bidirectionality of the auxiliary power supply and the integration of the auxiliary power supply circuit into the charging device provides the advantage that electrical power can be transferred by way of the auxiliary power supply from the electrical path of the charging device connected to the supply voltage input of the charging electronics unit to the path connected to the charging voltage input of the charging electronics unit and vice versa.
According to a preferred embodiment of the invention, the motor vehicle has a charging control unit for charging the high-voltage battery on the external alternating voltage source, and a charging connection can be made between the motor vehicle and the external alternating voltage source. The low-voltage battery feeds the supply voltage input of the control electronics unit and ensures that the charging control unit and the auxiliary power supply receive an electrical supply via the second interface of the auxiliary power supply.
In other words, the low-voltage battery supplies the charging electronics unit and the auxiliary power supply with electricity.
It is advantageous when the auxiliary power supply charges the link circuit capacitor in order to limit a switch-on current in the control electronics unit when the charging connection is made and the link circuit capacitor is charged.
The limitation of the switch-on current by systematic charging of the link circuit capacitor enables product-specific safety standards, which may be specified as part of the CE label for example, to be maintained. As well as product safety, limiting the switch-on current also has an advantageous effect on the reliability and longevity of the charging device.
According to a further embodiment, if the low-voltage battery is defective or deeply discharged and the charging connection to charge the high-voltage battery is made, the charging control unit can be supplied with electricity from the external voltage source by way of a control cable. The auxiliary power supply can be supplied with electricity from the external alternating voltage source via the first interface of the auxiliary power supply and feeds the supply voltage input of the charging electronics unit via the second interface of the auxiliary power supply.
This ensures that the high-voltage battery of the vehicle can also be charged via the external electrical network and the charging electronics unit in the absence of an electrical power output from the low-voltage battery. Although, in the normal operating case, the charging electronics unit is supplied by the low-voltage battery, the vehicle can still be charged in the event of a breakdown due to a defective or flat low-voltage battery. In the event of a breakdown, the charging control unit and the charging electronics unit are supplied from the external electrical network. Charging of the high-voltage battery therefore does not depend on the functionality of the low-voltage battery.
In addition, a DC chopper circuit can transform the electrical voltage between the high-voltage battery and the low-voltage battery, thus enabling the low-voltage battery to be charged by way of the DC chopper.
As a result of this embodiment, the low-voltage battery can likewise be charged by the external alternating voltage source in the event of a discharge or deep-discharge. Both the high-voltage battery and the low-voltage battery can therefore be charged in the event of a defective low-voltage supply internal to the vehicle. As a result, integrating the bidirectional power supply contributes to the robustness of the charging device, as a high availability for the customer is also achieved beyond the intended range of application of the charging device. The term robustness also implies that a fault scenario which has occurred can be rectified. With the embodiment described, this is so for the case of a discharged or deep-discharged battery on account of the re-charging of the low-voltage battery.
The invention is based on the following considerations. With electric vehicles, the high-voltage battery is usually charged by means of the charging device with an on-board charger, which is connected to the alternating current (AC) voltage network (e.g. domestic supply) by means of a special, standardized interface with logic and isolating contactors. The charger is supplied with the operating voltage via the vehicle's low-voltage on-board power supply. When the isolating contactors are closed, the switch-on current in the on-board charger must be limited in order to satisfy product-specific guidelines as part of the CE label. Various circuits, which complement the isolating contactors and which require a significant technical investment and, therefore, lead to an increasing complexity of the system, are known for this purpose. Further consequences are additional electrical losses in the vehicle's charging electrics and a degradation of the efficiency for charging the high-voltage battery.
An auxiliary power supply, which charges a link circuit capacitor by way of the vehicle's low-voltage battery before the isolating contactors are closed, can be incorporated as an improving measure. By this means, the switch-on current, which can also be referred to as inrush current, is limited. The CE conformity of the charging device can be achieved in this way. A further advantage, which likewise contributes to the robustness of the charging device, results if the auxiliary power supply is designed bidirectionally and is connected to the charger. For the designated exception where the on-board charger cannot be supplied from the low-voltage battery (e.g. due to the battery being deeply discharged or defective) and the link circuit capacitor cannot be charged, the charger can be supplied by the domestic supply via the auxiliary power supply. The vehicle can therefore be charged even when the low-voltage battery is flat. Other circuits, which are required to ensure that the high-voltage storage device can be charged when the low-voltage battery is discharged, can therefore be dispensed with. A robust charging device with high availability, low susceptibility to faults, and high safety standards can therefore be implemented with a bidirectional auxiliary power supply.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.